(1) Field of the Invention
The present invention relates to a snowmobile engine, in particular, relating to an arrangement and structure of auxiliaries in a snowmobile four-cycle engine. In more detail, the present invention is directed to an arrangement and structure of an alternator, oil filter and the like in a four-cycle engine mounted in a snowmobile.
(2) Description of the Prior Art
Conventionally, most snow vehicle such as snowmobiles and the like use two-cycle engines, which are relatively simple in structure, light and compact and yet powerful. Recently, however, because of regulation of exhaust gas or aiming at improvement in reduction of fuel consumption, there is a trend toward employing four-cycle engines. In contrast to two-cycle engines, which are compact and high in power, four-cycle engines need a camshaft and oil lubrication, inevitably tending towards large size. Further, since a four-cycle engine has to have valve gears for driving intake and exhaust valves and auxiliaries such as an oil filter for oil filtration, which also forces the engine to be large in size.
Taking these situations into account, in order to keep the engine room at the same size and shape as that when two-cycle engine is mounted, it is necessary to not only consider the oil pan configuration and the layout of intake and exhaust systems including the exhaust manifold but also closely examine the layout of associated auxiliaries such as the oil filter and the like.
It is necessary to provide a contrived layout of the oil pan configuration, intake and exhaust systems and associated auxiliaries, in order to make the body and engine hood of a snowmobile equipped with a four-cycle engine have a similar size to that of a two-cycle engine.
Also, as a generator for supplying electric power to the ignition and engine auxiliaries, a flywheel magneto and alternator are needed. Since this flywheel magneto is attached to the crankshaft end, the size of the engine in the shaft direction is enlarged, and the inertia of the crankshaft is increased, which leads to the disadvantage of lower acceleration performance.
The alternator is generally actuated by a belt which is driven by the drive force of the crankshaft. This arrangement enlarges the size of the engine perpendicular to the crankshaft, or the front-to-rear dimension, so that the alternator needs to be manipulatively and optimally laid out. It is also necessary to devise reduction of the front-to-rear dimension of the engine by optimizing the positional relationship between the alternator and the water pump which are both driven by the belt. When the engine is laid out in front of the steering shaft, there is a possibility of the steering shaft interfering with the auxiliaries such as alternator etc.
While the engine mounted in the snowmobile is covered by the engine hood, the flow of air is usually taken in to the engine room within the hood in order to cool the engine during travel. However, snow, together with the flow of air during travel, may sift into the engine room and cause trouble in the alternator, which is an electrical part. Therefore, the alternator is preferably disposed at a position away from influence snow during travel.
Further, a compact layout of these associated auxiliaries alone simply packs together the intake, exhaust systems and auxiliaries with the oil filter (which in particular needs frequent replacement), eliminating any spatial margin. Accordingly, replacement of the oil filter becomes impossible unless other parts arranged around the oil filter are removed, resulting in an increase in work load.